Intravascular diseases are commonly treated by relatively non-invasive techniques such as percutaneous transluminal angioplasty (PTA) and percutaneous transluminal coronary angioplasty (PTCA). These therapeutic techniques are well known in the art and typically involve the use of a balloon catheter with a guide wire, possibly in combination with other intravascular devices. A typical balloon catheter has an elongate shaft with a balloon attached proximate the distal end and a manifold attached to the proximal end.
In use, the balloon catheter is advanced over the guide wire such that the balloon is positioned adjacent a restriction in a diseased vessel. The balloon is then inflated and the restriction in the vessel is opened.
There are two basic types of balloon catheters used in combination with a guide wire, namely, over-the-wire (OTW) catheters and single-operator-exchange (SOE) catheters. The construction and use of both OTW catheters and SOE catheters are well-known in the art. An example of an OTW catheter may be found in commonly-assigned U.S. Pat. No. 5,047,045 to Arney et al. An example of an SOE balloon catheter is disclosed in commonly-assigned U.S. Pat. No. 5,156,594 to Keith.
PTA and PTCA catheters are preferably designed to optimize pushability, trackability and crossability. Pushability is defined as the ability to transmit force from the proximal end of the catheter to the distal end of the catheter. Trackability is defined as the ability to navigate tortuous vasculature. Crossability is defined as the ability to navigate the balloon catheter across narrow restrictions in the vasculature.
OTW balloon catheters may be classified into two groups. The first group comprising multi-lumen OTW balloon catheters, and the second group comprising coaxial OTW balloon catheters. Multi-lumen OTW catheters typically include a single extrusion shaft having two side-by-side longitudinally extending lumens, namely an inflation lumen and a guide wire lumen. By contrast, a coaxial OTW catheter typically includes two separate tubes, namely an inner tube and a coaxially disposed outer tube. The inner tube defines a guide wire lumen and an annular inflation lumen is defined between the inner tube and the coaxially disposed outer tube.
Prior art coaxial OTW-type balloon catheters have attempted to maximize pushability by incorporating a stainless steel outer tube on the proximal shaft portion (also referred to as a hypotube) and a polymeric distal shaft portion. Hypotubing is, however, prone to kinking. Coaxial OTW-type balloon catheters can also incorporate a polymer shaft or a reinforced polymer shaft as a proximal shaft portion (e.g. composite) as a compromise between maximizing pushability and minimizing the probability of kinking in the proximal shaft portion.
The trackability of a particular catheter design is analyzed in terms of the trackability of the distal portion of the catheter, as this portion must track the guidewire through small tortious vessels to reach the stenosed area to be treated. A more flexible distal portion has been found to improve trackability. Further, in transitioning from a stiff proximal segment or portion of the catheter shaft to a more flexible distal portion of the catheter shaft, it has been found that kinking readily occurs at the joint between the two shaft segments of differing flexibility. The increased flexibility of the distal section also makes this portion of the catheter less able to be pushed from the proximal end of the catheter.
Pushability without kinking, trackability and crossability are all features desirable in a catheter design. However, factors which improve one feature, such as pushability, can have a detrimental impact on trackability and vice versa. There is an unmet need for a coaxial over-the-wire type balloon catheter which incorporates features that provide improved pushability without kinking and an improved trackability in order to cross tight lesions in tortious anatomy.